1. Field of the Invention
The present invention relates, in general, to a polyolefinic blend and process for preparing the same, and more particularly, to a homogeneous polyolefinic blend with a barrier property having low organic liquid and vapor permeability, as well as to an easy process for preparing the homogeneous polyolefinic blend with ordinary processing equipment.
2. Description of Prior Art
There are many patents that aim at improving barrier properties to fluid, for example, the barrier properties of blends of polyolefin and other polymers to organic liquid and vapor.
U.S. Pat. No. 4,410,482 discloses a process for preparing a heterogeneous blend of polyolefin and polyamide by low shear mixing. In this patent, the polyamide is present in the article as a multitude of thin, substantially two-dimensional, parallel and overlapping layers of material (as shown in FIG. 1A). An alkylcarboxyl-substituted polyolefin is used as a compatibilizer which is present between the layers and adheres them together. It is necessary to use low shear mixing when processing the heterogeneous blend. Therefore, it is difficult for the heterogenous blend to be manufactured into an article using ordinary high shear mixing processing equipment. Such a heterogeneous blend will not ordinarily have wide application to commercial processing equipment, unless the equipment is redesigned or modified.
European Patent Laid-Open Patent No. 0 238 197 suggests a preparation process for a homogeneous blend by high shear mixing which is capable of manufacturing an article having an improved barrier property to organic liquid and vapor permeability using ordinary processing equipment. The aim is to overcome the difficulty attributable to the low shear mixing processing conditions in preparing the above-stated heterogeneous blend.
Polymer blends with barrier properties having low organic liquid and vapor permeability are obtained by blending an organic liquid and vapor-permeable polymer with an organic liquid and vapor barrier polymer to form a discrete dispersion of the polymers in each other. This causes the organic liquid and vapor permeable polymer to undergo branching or a limited amount of cross-linking with an increase of viscosity sufficient to cause the polymers to separate into distinct phases composed of larger particles. This results in a homogeneous blend which has an improved barrier property to organic liquid and vapor.
A significant disadvantage of this European patent is that the organic liquid and vapor-permeable polymer should be partially cross-linked in a substantial amount (as much as the added amount of the coupling agent, 0.01 to 1% by weight) to obtain the homogeneous blend. The processability of the resulting blend is inevitably degraded when it is manufactured into a blown film. The resulting blown film also shows inferior mechanical properties. As shown in FIG. 1B, the morphology of the homogeneous blend is disc-like.
Korean Pat. Appln. No. 91-13347 "Polyolefinic blend comprising reactive low molecular weight compound and preparation process thereof" is a prior invention by the present applicant, which describes a heterogeneous blend similar in content to the present invention. This heterogeneous blend does not exhibit appropriate processability when it is manufactured into a film in ordinary processing equipment, and the resulting articles do not have the desired mechanical properties. Such disadvantages are overcome in the present invention, which is completely different from the prior invention by employing a polymeric compatiblizer which was not used in the prior invention.
The expression "heterogeneous blend" as used in this specification means that the organic liquid and vapor permeable polymer form a distinct phase. As shown in FIG. 5, polyolefin and a polymer with a barrier property having low organic liquid and vapor permeability have distinct phases. On the other hand, the expression "homogeneous blend" denotes that the polymer with barrier property having low organic liquid and vapor permeability is uniformly distributed in, for example, the polyolefin phase. This is shown in FIG. 2.